fix typo for server create in server.rst
fix typo for server create in server.rst

we have <security-group-list> in server create option,
while <security-group-name> in the explanation, they
both should be <security-group-name>.

Closes-Bug: #1466742
Change-Id: I26a25f57e57d8f9e19ec9c9ccb3c2b8d5396b78d

dtroyer/python-openstackclient,dtroyer/python-openstackclient,redhat-openstack/python-openstackclient,redhat-openstack/python-openstackclient,openstack/python-openstackclient,openstack/python-openstackclient,BjoernT/python-openstackclient,BjoernT/python-openstackclient